EUBACTERIUM-YURII SUBSPECIES MARGARETIAE IS RESISTANT TO NONOPSONIC PHAGOCYTIC INGESTION

We have previously shown that strains of Eubacterium yurii are hydroph obic, as compared with human polymorphonuclear leukocytes (PMNs), poss ibly because of a crystalline surface layer (S-layer) covering the cel l envelope of this potential endo-perio pathogen. The aim of the prese nt study was to investigate the phagocytic ingestion by PMNs of the th ree E. yurii subspecies, with special attention to bacterial surface s tructures and hydrophobicity. Type strains of subspp. margaretiae, yur ii, and schtitka, together with three clinical isolates from necrotic root canals, were studied. All strains were hydrophobic when tested by a two-phase partition method. E. yurii subspp. margaretiae strains AT CC43715T, ES4C, and ES14B-8E were resistant to PMN ingestion in the ab sence of opsonins, whereas strains of the two other subspecies were re adily ingested. The presence of a resistant strain (subsp. margaretiae ATCC43715T) did not inhibit the ingestion of a sensitive strain (subs p. schtitka ATCC43716T). Ingestion of E. yurii subsp. margaretiae stra ins required opsonization by normal human serum or specific antibodies . Electron microscopy revealed an S-layer in all strains and fimbria-l ike structures in the subspp. margaretiae and yurii strains. The antis erum prepared against the S-protein of E. yurii subsp. margaretiae ATC C43715T showed only slight cross-reactivity with other E. yurii strain s and indicated the presence of strain-specific rather than species- o r subspecies-specific antigens in the S-protein of E. yurii subsp. mar garetiae ATCC43715T. The results suggest that the mere presence of the S-layer or fimbria-like structures cannot explain the susceptibility to ingestion by the PMNs. It is possible that specific-receptor-mediat ed binding overrides the importance of hydrophobicity in the nonopsoni c phagocytosis of E. yurii subspecies.